1. Field of the Invention
The present invention is directed toward the field of discrete filters, and more particularly toward capacitor and/or inductor bank filters.
2. Art Background
Inductor and capacitor banks may be configured to implement many different types of discrete filters. FIG. 1a illustrates one embodiment for an inductive (L) bank. For this embodiment, the inductive bank includes five inductors (110, 108, 106, 104 and 102). Although inductive bank 100 includes five inductors, any number of inductors may be used without deviating from the spirit or scope of the invention. The number and values for the inductors is a function of the desired frequency response characteristics of the filter. The inductors, which form inductive bank 100, are configured in parallel. Each inductor is added to the L bank through a corresponding switch as shown in FIG. 1a. Typically, the switches are implemented using metal oxide semiconductor (“MOS”) transistors.
FIG. 1b illustrates one embodiment for a capacitive bank. For this example, capacitive bank 120 contains five capacitors (130, 128, 126, 124 and 122). A different number of capacitors and different capacitive values may be selected to implement different frequency responses. Also, as shown in FIG. 1b, capacitors 128, 126, 124 and 122 are selected for the C bank through a respective switch. Typically, these switches are implemented with MOS transistors.
Each MOS switching transistor introduces a resistive component into the filter response. Thus, each capacitor selected in the C bank increases the series resistance. The increase in series resistance, or decrease in parallel resistance, decreases the Q factor, which, in turn, degrades performance of the filter bank.
Accordingly, it is desirable to improve the characteristics and performance of an LC filter by reducing parasitic capacitance and increasing the Q factor.